Traditional helicopter control systems employ a cyclic stick for longitudinal and lateral blade pitch control, pedals for directional yaw control and a pivotable collective stick for collective blade pitch or lift control. With advancement in technology, these control functions were combined into a single control stick of the type disclosed in Diamond et al U.S. Pat. No. 4,420,808, issued in 1983 and owned by Assignee, which discloses a single side arm controller that provides control signals in each of the pitch, roll, yaw, and collective/lift axes of a helicopter control system. The stick is essentially a "force" stick and there is limited displacement of the stick in each axis. Such a control stick is typically used in a fly-by-wire flight control system. Because of the minimal displacement of this control stick, there is little tactile feedback from the stick to the pilot, particularly in the collective channel, so as to permit the pilot to accurately perceive the extent of collective pitch input and, hence, the amount of collective pitch reserve available to the pilot without diverting pilot attention to a secondary cue within the cockpit, such as torque or collective position indicators. The proprioceptive cues received by the pilot from the Diamond et al single side arm controller are adequate for yaw and cyclic pitch maneuvers in as much as the helicopter's agility and response is nearly instantaneous in response to stick movement, since little energy is required to bank or yaw the helicopter. However, the helicopter's lift/collective Z-axis response necessitates a substantial change in the energy state and is characterized by a long time constant. Therefore, in the absence of a physical cue which may be sensed by the pilot, such as control stick displacement, the full authority multi-axis single side arm controller of Diamond et al is not particularly well suited to rotor craft which must perform in a flight mode in which the tactile feedback or pilot feel is critical in the collective channel, such as aircraft to be used in nap-of-the-earth flights.
To accommodate aircraft which must perform these collective pitch sensitive flights, Wright et al U.S. Pat. No. 4,696,445, granted in 1987 and owned by Assignee, utilized a separate collective stick in concert with the side arm controller in which the pilot has the option of effecting all helicopter controls through the side arm controller or using the separate collective stick to control collective pitch during collective channel sensitive flights. The displacement collective control stick disclosed in the Wright et al patent is the conventional pivotal type consisting of a pilot grip positioned at the end of a long stick member which is pivotally connected at its opposite end to a fixed point in the aircraft.
This lengthy prior art collective stick has the advantage that the pilot grip moves about a large radius such that its motion is virtually linear. The advantage of this virtually linear motion of the hand grip of the collective stick is that it reduces the pilot fatigue caused by excessive wrist articulation in that it makes it easier for the pilot to locate and operate the various push-button controls positioned on the face of the hand grip.
While this displacement type collective stick offers the pilot the desired physical displacement cues indicative of the magnitude of collective input, it occupies substantial space in the cockpit since the stick is approximately two feet long. Therefore, a collective stick of this prior art type is not acceptable in certain modern helicopters in which the objective is to down size the cockpit.